[libc-commits] [PATCH] D154494: [libc] Adding a version of memcpy w/ software prefetching

[Guillaume Chatelet via Phabricator via libc-commits]

gchatelet created this revision.
gchatelet added reviewers: sivachandra, courbet.
Herald added subscribers: libc-commits, pengfei.
Herald added projects: libc-project, All.
gchatelet requested review of this revision.

For machines with a lot of cores, hardware prefetchers can saturate the memory bus when utilization is high.
In this case it is desirable to turn off the hardware prefetcher completely.
This has a big impact on the performance of memory functions such as `memcpy` that rely on the fact that the next cache line will be readily available.

This patch adds the 'LIBC_COPT_MEMCPY_X86_USE_SOFTWARE_PREFETCHING' compile time option that generates a version of memcpy with software prefetching. While not fully restoring the original performances it mitigates the impact to an acceptable level.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D154494

Files:
  libc/src/string/CMakeLists.txt
  libc/src/string/memory_utils/op_builtin.h
  libc/src/string/memory_utils/x86_64/memcpy_implementations.h
  utils/bazel/llvm-project-overlay/libc/BUILD.bazel

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